linux-kernel - [boot crash] Re: [PATCH 2.6.27-rc5 re-resubmit] Fix itimer/many thread hang.

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Message-ID: <20080923125238.GA25042@elte.hu>
Date:	Tue, 23 Sep 2008 14:52:39 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frank Mayhar <fmayhar@...gle.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: [boot crash] Re: [PATCH 2.6.27-rc5 re-resubmit] Fix itimer/many
	thread hang.


* Ingo Molnar <mingo@...e.hu> wrote:

> * Frank Mayhar <fmayhar@...gle.com> wrote:
> 
> > This is the second resubmission of the posix timer rework patch, 
> > posted a few days ago.  This includes the changes from the previous 
> > resubmittion, which addressed Oleg Nesterov's comments, removing the 
> > RCU stuff from the patch and un-inlining the thread_group_cputime() 
> > function for SMP.  In addition, per Ingo Molnar it simplifies the UP 
> > code, consolidating much of it with the SMP version and depending on 
> > lower-level SMP/UP handling to take care of the differences.  It also 
> > cleans up some UP compile errors, moves the scheduler stats-related 
> > macros into kernel/sched_stats.h, cleans up a merge error in 
> > kernel/fork.c and has a few other minor fixes and cleanups as 
> > suggested by Oleg and Ingo.  Thanks for the review, guys.
> 
> below is the delta patch i've applied to tip/timers/posixtimers - might 
> be easier to review for those who've seen v1 and who'd like to check the 
> changes.
> 
> i've also merged v2 into tip/master and started testing it.
> 
> 	Ingo
> 
> ---------------->
> From bb34d92f643086d546b49cef680f6f305ed84414 Mon Sep 17 00:00:00 2001
> From: Frank Mayhar <fmayhar@...gle.com>
> Date: Fri, 12 Sep 2008 09:54:39 -0700
> Subject: [PATCH] timers: fix itimer/many thread hang, v2
> 
> This is the second resubmission of the posix timer rework patch, 
> posted a few days ago.

-tip testing found a boot crash on a 32-bit x86 test system, and i've 
bisected it down to this commit. I've attached the .config. The box is 
hard to debug and the crash happens very early so there's no log - but 
it was reproducible so you should be able to trigger it by doing this 
in the tip tree:

  git checkout 788222bf3d6d7ee08ce308f078c8774eb896c59e

[ that is the -tip tree just before the revert commit. ]

... and use the attached .config to build a test kernel and to reproduce 
the crash. (it doesnt matter if it wont fully boot on your testbox - the 
crash happen very early)

here is how you can access the tree:

  http://people.redhat.com/mingo/tip.git/README

i also found a boot hang on a 64-bit x86 test system - that too is 
solved with this revert. I've attached that config too.

The common theme in both configs is that they are !SMP - and many 
updates in v2 relate to !SMP details, so i'd suspect a bug in that area.

( and thanks to working with delta patches i was able to fall back to 
  the v1+fixes state in tip/timers/posix-timers, instead of having to 
  drop/revert the whole work. So please update this stuff with delta 
  patches in the future. )

	Ingo

View attachment "config" of type "text/plain" (56461 bytes)

View attachment "config64" of type "text/plain" (56628 bytes)